From 3c70d60c4fe818879ba953530edd4a902b5d9a05 Mon Sep 17 00:00:00 2001
From: Gurinder Singh <frederick.the.fool@gmail.com>
Date: Tue, 19 Mar 2024 09:20:23 +0530
Subject: [PATCH] Gracefully handle AnonConst in diagnostic_hir_wf_check()

when it is the default value of a generic param
---
 .../rustc_hir_analysis/src/hir_wf_check.rs    | 10 ++++
 ...ce-hir-wf-check-anon-const-issue-122199.rs | 12 ++++
 ...ir-wf-check-anon-const-issue-122199.stderr | 60 +++++++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs
 create mode 100644 tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.stderr

diff --git a/compiler/rustc_hir_analysis/src/hir_wf_check.rs b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
index 2a9101b3808fa..18848702fea69 100644
--- a/compiler/rustc_hir_analysis/src/hir_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
@@ -163,6 +163,16 @@ fn diagnostic_hir_wf_check<'tcx>(
                 kind: hir::GenericParamKind::Type { default: Some(ty), .. },
                 ..
             }) => vec![*ty],
+            hir::Node::AnonConst(_)
+                if let Some(const_param_id) =
+                    tcx.hir().opt_const_param_default_param_def_id(hir_id)
+                    && let hir::Node::GenericParam(hir::GenericParam {
+                        kind: hir::GenericParamKind::Const { ty, .. },
+                        ..
+                    }) = tcx.hir_node_by_def_id(const_param_id) =>
+            {
+                vec![*ty]
+            }
             ref node => bug!("Unexpected node {:?}", node),
         },
         WellFormedLoc::Param { function: _, param_idx } => {
diff --git a/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs b/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs
new file mode 100644
index 0000000000000..107cfbb9ff699
--- /dev/null
+++ b/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs
@@ -0,0 +1,12 @@
+trait Trait<const N: Trait = bar> {
+//~^ ERROR cannot find value `bar` in this scope
+//~| ERROR cycle detected when computing type of `Trait::N`
+//~| ERROR cycle detected when computing type of `Trait::N`
+//~| ERROR `(dyn Trait<{const error}> + 'static)` is forbidden as the type of a const generic parameter
+//~| WARN trait objects without an explicit `dyn` are deprecated
+//~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+    fn fnc(&self) {
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.stderr b/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.stderr
new file mode 100644
index 0000000000000..2d5a0ede962b2
--- /dev/null
+++ b/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.stderr
@@ -0,0 +1,60 @@
+error[E0425]: cannot find value `bar` in this scope
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:30
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |                              ^^^ not found in this scope
+
+warning: trait objects without an explicit `dyn` are deprecated
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:22
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |                      ^^^^^
+   |
+   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: `#[warn(bare_trait_objects)]` on by default
+help: if this is an object-safe trait, use `dyn`
+   |
+LL | trait Trait<const N: dyn Trait = bar> {
+   |                      +++
+
+error[E0391]: cycle detected when computing type of `Trait::N`
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:22
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |                      ^^^^^
+   |
+   = note: ...which immediately requires computing type of `Trait::N` again
+note: cycle used when computing explicit predicates of trait `Trait`
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:1
+   |
+LL | trait Trait<const N: Trait = bar> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
+
+error[E0391]: cycle detected when computing type of `Trait::N`
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:13
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |             ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: ...which immediately requires computing type of `Trait::N` again
+note: cycle used when computing explicit predicates of trait `Trait`
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:1
+   |
+LL | trait Trait<const N: Trait = bar> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
+
+error: `(dyn Trait<{const error}> + 'static)` is forbidden as the type of a const generic parameter
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:22
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |                      ^^^^^
+   |
+   = note: the only supported types are integers, `bool` and `char`
+
+error: aborting due to 4 previous errors; 1 warning emitted
+
+Some errors have detailed explanations: E0391, E0425.
+For more information about an error, try `rustc --explain E0391`.